Police launched an investigation into the distribution of illegal material via Amazon’s Japanese store after arresting two men in September 2013 for selling illegal photo books. Since then, an Amazon distribution centre in Kanagawa has been raided in November last year, before police entered the Tokyo site on 23 January.

Police in the Asian country are intensifying their efforts to thwart child abuse, after a new law was passed in June 2014 forbidding the possession of real images of child sexual abuse. However, creating and sharing such images has been illegal since 1999.

Despite this, the popularity of Japan’s “idol industry” often makes it difficult to classify images as illegal. Idol culture often features young bands and models, many of which are aged between 14 and 16, in suggestive poses.

It’s extremely difficult to say whether these materials can be classified as child pornography," Ryoji Mori, a Japanese attorney told Business Week. “It’s obvious that the target audience is paedophiles, but the manufacturers have done it in such a way that it’s difficult to say if it’s illegal."

The Japanese sites of Amazon and Yahoo both had products associated with the idol industry available as recently as October last year.

Amazon has responded to the latest raid on its Tokyo office in a statement online emphasising its proactive removal of illegal items.